Epoxy bonded steel plates for strengthening of concrete structures were introduced to the construction industry in the late 1960’s, the use of fiber reinforced polymers (FRP’s) in the 1990’s. Therefore, these materials are used now in construction already for 50 and 25 years, respectively. The monitoring of such applications in construction is very important and gives more confidence to this strengthening technique. In this paper, two different long-term monitoring campaigns over an extraordinary long duration will be presented. Firstly, a 47-year monitoring campaign on a concrete beam with an epoxy bonded steel plate and secondly, a 20-year monitoring campaign on a road bridge with epoxy bonded CFRP strips.